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166 lines
4.6 KiB
166 lines
4.6 KiB
// -----------------------------------------------------------------------------
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// MICS-2710 (and MICS-4514) NO2 Analog Sensor
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// Copyright (C) 2019 by Xose Pérez <xose dot perez at gmail dot com>
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// -----------------------------------------------------------------------------
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#if SENSOR_SUPPORT && MICS2710_SUPPORT
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#pragma once
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#include <Arduino.h>
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#include "BaseAnalogSensor.h"
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extern "C" {
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#include "../libs/fs_math.h"
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}
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class MICS2710Sensor : public BaseAnalogSensor {
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public:
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// ---------------------------------------------------------------------
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// Public
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// ---------------------------------------------------------------------
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MICS2710Sensor() {
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_count = 2;
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_sensor_id = SENSOR_MICS2710_ID;
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}
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void calibrate() {
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setR0(_getResistance());
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}
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// ---------------------------------------------------------------------
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void setAnalogGPIO(unsigned char gpio) {
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_noxGPIO = gpio;
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}
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unsigned char getAnalogGPIO() {
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return _noxGPIO;
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}
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void setPreHeatGPIO(unsigned char gpio) {
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_preGPIO = gpio;
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}
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unsigned char getPreHeatGPIO() {
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return _preGPIO;
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}
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// ---------------------------------------------------------------------
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// Sensor API
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// ---------------------------------------------------------------------
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// Initialization method, must be idempotent
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void begin() {
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// Set NOX as analog input
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pinMode(_noxGPIO, INPUT);
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// Start pre-heating
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pinMode(_preGPIO, OUTPUT);
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digitalWrite(_preGPIO, HIGH);
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_heating = true;
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_start = millis();
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_ready = true;
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}
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// Pre-read hook (usually to populate registers with up-to-date data)
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void pre() {
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// Check pre-heat time
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if (_heating && (millis() - _start > MICS2710_PREHEAT_TIME)) {
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digitalWrite(_preGPIO, LOW);
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_heating = false;
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}
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if (_ready) {
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_Rs = _getResistance();
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}
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}
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// Descriptive name of the sensor
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String description() {
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return String("MICS-2710 @ TOUT");
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}
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// Descriptive name of the slot # index
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String description(unsigned char index) {
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return description();
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};
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// Address of the sensor (it could be the GPIO or I2C address)
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String address(unsigned char index) {
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return String("0");
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}
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// Type for slot # index
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unsigned char type(unsigned char index) {
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if (0 == index) return MAGNITUDE_RESISTANCE;
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if (1 == index) return MAGNITUDE_NO2;
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return MAGNITUDE_NONE;
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}
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// Current value for slot # index
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double value(unsigned char index) {
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if (0 == index) return _Rs;
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if (1 == index) return _getPPM();
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return 0;
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}
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private:
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unsigned long _getReading() {
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return analogRead(_noxGPIO);
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}
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double _getResistance() {
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// get voltage (1 == reference) from analog pin
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double voltage = (float) _getReading() / 1024.0;
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// schematic: 3v3 - Rs - P - Rl - GND
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// V(P) = 3v3 * Rl / (Rs + Rl)
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// Rs = 3v3 * Rl / V(P) - Rl = Rl * ( 3v3 / V(P) - 1)
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// 3V3 voltage is cancelled
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double resistance = (voltage > 0) ? _Rl * ( 1 / voltage - 1 ) : 0;
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return resistance;
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}
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double _getPPM() {
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// According to the datasheet (https://www.cdiweb.com/datasheets/e2v/mics-2710.pdf)
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// there is an almost linear relation between log(Rs/R0) and log(ppm).
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// Regression parameters have been calculated based on the graph
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// in the datasheet with these readings:
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//
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// Rs/R0 NO2(ppm)
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// 23 0.20
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// 42 0.30
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// 90 0.40
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// 120 0.50
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// 200 0.60
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// 410 0.90
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// 500 1.00
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// 1000 1.30
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// 10000 5.00
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return fs_pow(10, 0.5170 * fs_log10(_Rs / _R0) - 1.3954);
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}
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bool _heating = false;
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unsigned long _start = 0; // monitors the pre-heating time
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unsigned char _noxGPIO = MICS2710_PRE_PIN;
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unsigned char _preGPIO = MICS2710_NOX_PIN;
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};
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#endif // SENSOR_SUPPORT && MICS2710_SUPPORT
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